1. Field of the Invention
The present invention relates to a wireless base station, a mobile station, a radio communication system, and a radio communication method.
2. Related Background of the Invention
A mobile communication system using OFDMA (Orthogonal Frequency Division Multiple Access) which realizes multiple access between a wireless base station and a mobile station by dividing a carrier signal into a plurality of orthogonal sub-carriers, have been known. Details of the communication scheme are described in the following Non-Patent Document 1. As a channel assignment scheme in the mobile communication system using OFDMA, two schemes illustrated in FIGS. 15A and 15B are included. In the scheme illustrated in FIG. 15A, sub-carriers having the same frequency band are assigned to sectors S1, S2 and S3 in one wireless base station, respectively, and in the scheme illustrated in FIG. 15B, frequency band is logically divided into three segments, and sub-carriers belonging to each of the divided segments are assigned to the neighboring sectors S1, S2 and S3, respectively.
Moreover a channel assignment scheme has been disclosed, where a cell C1 corresponding to one base station are divided into two areas of an outer area A1 and an inner area A2, and to the inner area A2 having few interference with other cells, all transmittable sub-carriers are assigned, and to the outer area A1 having much interference with other cells, segment divided parts of sub-carriers are assigned (refer to the following Patent Document 1 and FIG. 16).    Patent Document 1: Japanese Patent Application Laid-open No. 2005-80286    Non-Patent Document 1: “IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1”, IEEE Std, February 2006